The present invention relates generally to signal processing systems and methods and more particularly to systems and methods for processing audio signals in an audio/visual (A/V) recording device to remove abrupt changes in volume.
In a typical A/V recording system, a user is able to pause and resume recording of an A/V program. For example, a user may desire to xe2x80x9cpausexe2x80x9d while recording a television program when a commercial begins. Selecting pause will cause the audio level recorded to change instantly from the current level to zero. When the program resumes and xe2x80x9cresumexe2x80x9d recording is selected by the user, the audio level will change instantly from zero back to the current level. Such abrupt transitions in the recorded audio signal will typically produce a noticeable xe2x80x9cclickxe2x80x9d in the playback audio.
Accordingly, it is desirable to provide systems and methods for processing audio signals in an A/V recording device so as to remove noticeable abrupt transitions, such as xe2x80x9cclicksxe2x80x9d, in the playback audio.
The present invention provides signal processing systems and methods for removing undesirable transitions in an audio signal, and more particularly for smoothing out discontinuous, abrupt changes in amplitude in an audio signal, such as abrupt changes in volume from the current level to zero and back to the current level. The present invention is particularly useful for processing audio signals during encoding in an A/V recording device.
According to the invention, digital signal processing systems and methods are provided for smoothing out an audio signal having an abrupt transition in volume. A DSP in an audio visual recording device is configured to smooth out discontinuous volume transitions in an audio signal during encoding. Such abrupt, discontinuous changes can occur when a user instructs the recording device to pause and resume during recording or when the user changes channels during recording. The DSP applies a transform that linearly increases or decreases the volume over one or more audio frames from the first volume level to the next volume level after the abrupt change.
According to an aspect of the present invention, a method of smoothing an audio signal having a volume discontinuity is provided. The method typically includes receiving a digital input signal, wherein the digital input signal represents an analog audio signal sampled a number of times during each of a plurality of frames, and wherein the digital input signal has a discontinuous volume change from a first value to a second value. The method also typically includes applying a transform to the digital input signal to produce a digital output signal having a continuous volume change from the first value to the second value over one or more frames, wherein the transform is a function of the number of samples during a frame and the difference between the first and second values.
According to another aspect of the invention, a method of smoothing an audio signal having a volume discontinuity is provided. The method typically includes sampling an input analog audio signal a number of times during each of a plurality of frames to produce a digital signal, wherein the audio signal includes a discontinuous volume change from a first value to a second value during a first frame. The method also typically includes applying a transform to the digital signal to produce a digital output signal having a continuous volume change from the first value to the second value over one or more frames, wherein the transform is a function of the number of samples taken during a frame and the difference between the first and second values.
According to yet another aspect of the present invention, a device for encoding and recording an audio signal is provided. The device typically includes a first buffer that stores one or more frames of digital audio data representing an analog audio signal sampled a number of times during each of a plurality of frames, wherein the first buffer receives and stores a first frame of digital audio data having a discontinuous volume change from a first level to a second level. The device also typically includes a first digital signal processor coupled to the first buffer and configured to smooth out the discontinuous change in volume, wherein the first digital signal processor applies a transform to the first frame of digital audio data to produce a digital output signal having a continuous volume change from the first level to the second level over one or more frames, wherein the transform is a function of the number of samples taken during each frame and of the first and second levels.
Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.